Conversion of hydrocarbon oils



FRACTaONAToR FRACTIONATOR `lala. 7", 1941.

5 soAKlNG DRUMS R. F. TROW CONVERSION OF HYDROCARBON OILS Filed sept. 8, '193s FRESH CHARGE ATTORNEYS Patented Jan. 7, 1941 UNITED STATES PATENT OFFICE Richard F. Trow, Tuckahoe, N. Y., assigner to The Texas Company, New York, N. Y., a corporation of Delaware Application September 8, 1938, Serial No. 228,881

2 Claims.

This invention relates to the conversion of hydrocarbon oils, and has to do particularly with a process for the cracking of hydrocarbon oils utilizing the principle of gas reversion.

5 In accordance with the invention, hydrocarbon cil of relatively non-refractory character is subjected to cracking conditions of temperature and pressure to produce normally gaseous hydrocarbons and relatively refractory or cyclic heavier materials suitable for further conversion. The more refractory stocks are separately processed in an independently controlled cracking operation under gas reversion conditions.

When operating on a virgin stock, particularly in a once-through operation or in the absence of large amounts of recycle stock, it is unnecessary to employ gas reversion to obtain conditions whereby large yields and high crack `per pass are possible. On the other hand, it has been found that gas reversion reactions, wherein normally gaseous hydrocarbons are converted into normally liquid hydrocarbons in the presence of the hydrocarbon oil undergoing cracking, may be more efciently carried out under the conditions prevailing in a system operating on refractory or cyclic stocks. It is an object of the present invention, therefore, to segregate the more refractory or cyclic stocks and s-eparately convert these under gas reversion conditions whereby the U benefits of the present invention are more fully realized.

The invention will be more fully understood from the following description to be read in connection with the accompanying drawing showing 30 a diagrammatic sketch of one form of apparatus for carrying out the process of the invention.

Referring to the drawing, a fresh charging stock of the less refractory type, such as reduced crude or straight run distillate, preferably a vir- 40 gin gas oil, is introduced through the line I by the pump 2. The charge is passed through the line 3 and, combined with a reflux condensate drawn from the lower portion of the fractionator 5 through line 6. Any amount of the charge may be introduced through the branch line 8 into the fracticnator as a reflux medium to produce suiii- `cient reflux condensate or recycle stock to prevent cokelformation in the cracking system, to provide adequate heat, and to produce the de- U') sired cracking of the heavy fractions of fresh charge.

The mixture of fresh charge and reflux condensate is forced by the pump 9 through the line II) to a heating coil I I located in a furnace I2. In the heating coil, the oil is subjected, to cracking conditions of temperature and pressure at a relatively high crack per pass so as to avoid coking diiiiculties or excess gas formation. Ordinarily, the temperatures may range around 900 to 1000D F. and pressures of about 200 to 1000 5 pounds. Hot products are transferred from the coil II through the line I4 to a soaking drum I5 wherein the products pass downwardly therethrough to the bottom and then through a line lli to a second soaking drum I'l. While two l0 soaking drums are shown, it is understood that any number may be used. These soaking drums are maintained preferably above 250 pounds pressure, and ordinarily only slightly lower in temperature and pressure than those prevailing in the coil II. The unvaporized residue is continuously drawn off from the lower portion of the soaking drum Il through the line I8 in order to maintain a low liquid level therein.

The vapors pass upwardly through the soaking drum I'I and are conducted from the upper portion thereof through the line 20 to the fractionator 5. A substantially reduced pressure may be maintained on the fractionator by manipulation of the valve I9 in the line 20. The 25 vapors enter the lower portion of the fractionator and some fractionation takes place below the tray 2| to produce sufcient heavy reflux condensate to balance out the operation. The uncondensed vapors pass up through the conduit in the tray .30 2I and undergo further fractionation in the upper portion of the fractionator. Substantially all the constituents of higher boiling point range than gasoline are'condensed as a reiiux condensate and collect on the tray ZI from which they are withdrawn through the line 22. Gasoline vapors and normally gaseous hydrocarbons pass overhead from the fractionator 5 through the line 24 and condenser 25 to a receiver 26 which is equipped with a gas release line 21 and 40 gasoline drawoff line 28.

The residuum drawn olf from the soaking drum Il through the line I8 is discharged under reduced pressure into the lower portion of a tar stripper 30 wherein flash distillation takes place. 45 An unvaporized heavy residuum or fuel oil is vdrawn from the lower portion of the tar stripper through line 3l. The vapors are fractionated in the upper portion of the tar stripper to produce a cyclic or refractory condensate which is collected on the tray 33. The refractory recycle stock from the fractionator 5, which is drawn off through the line 22, is also introduced into the upper section of the tar stripper and collects on the tray 33. Uncondensed vapors comprising gasoline and normally gaseous hydrocarbons are withdrawn from the upper portion of the tar stripper through the line 34 and introduced into a receiver 35 provided with a liquid drawoif line 36 and gas release line 31.

The cyclic gas oil is withdrawn from the pan 33 in the tar stripper through a line 40 and forced, all or in part, by pump 4I through a cooler 42 into the upper portion of an absorber 44. Any excess of the gas oil not introduced in the absorber may be withdrawn through the branch line 43. In the absorber, the oil is used as the scrubbing medium for absorbing the heavier constituents such as hydrocarbons between two and live carbon atoms, from the gases of the system introduced into the lower portion of the absorber through the line 4 5.

The unabsorbed gases are released from-the upper portion of the absorber through the line 41. The enriched oil is withdrawn from the lower portion of the absorber through the line 48 in which is located a pump 49. The line 48 communicates with a recycle line 50 whereby the oil is passed to heating coil 5I located in a furnace 52. Any excess oil withdrawn through the branch line 43 is also introduced into the line 50 leading to the heating coil 5l.

In the coil 5i, the mixture of cycle gas oil and normally gaseous hydrocarbons is subjected to conversion conditions of temperature and pressure which should be as drastic as possible to obtain maximum conversion without coking diniculties, for example 900 to 1100* F, and 200 to 800 pounds. Hot products are transferred through the line 54 to a soaking drum 55 through which they pass downwardly and are withdrawn from the lower portion thereof through the line 56 to a second soaking drum 51. The soaking drums are maintained, preferably under pressures in excess of 200 pounds per square inch and ordinarily conditions of temperature and pressure slightly lower than those prevailing in the heating coil 5|.

In the soaking drum 51 unvaporized residuurn separates and is continuously withdrawn therefrom, so as to maintain a low liquid level, through the tar line 58 leading to the tar stripper 38 wherein the residuum is introduced therein under reduced pressure for flash distillation. The vapors pass upwardly through the soaking drum 51 and are conducted from the upper portion thereof through the vapor line 68 to a fractionator 6| wherein the constituents of higher boiling point gasoline are condensed as a reflux condensate to produce a recycle stock which is withdrawn from the lower portion thereof through the line 82 and forced by the pump 83 through the line 50 to the heating coil 5I. The vapors comprising gasoline and normally gaseous hydrocarbons are withdrawn from the upper portion of the fractionator 6l through the vapor line B5 and condenser 8B to an accumulator 81 provided with a gas release line 63 and liquid drawoff line 69.

The gaseous hydrocarbons released from the receiving drums 2B and 81 through lines 21 and 68, respectively, are merged in the line 45 and passed to the absorber 44. Unstabilized gasolines, collected in the receivers and 61, are withdrawn through the liquid drawoff lines 28 and 69, respectively, and merged in the line 10, and passed to a stabilizer 12 wherein hydrocarbons more volatile than those desired in the nished gasoline are fractionated out. The stable gasoline is Withdrawn from the lower portion of the stabilizer through line 14. The vapors are taken overhead from the stabilizer through the line 16 and condenser 11 to receiver 13. The condensate collecting in the receiver 18 is withdrawn through the line 19 and a portion thereof may be passed through the branch line 80 by the pump 8| to the upper portion of the stabilizer as a reux. The remainder of the condensate is forced by the pump 84 through the line 85 which communicates with the line 50 leading to the heating coil 5i. This condensate or stabilizer reflux, comprising mainly C3 and C4 hydrocarbons, undergoes gas reversion in admixture with the refractory recycle stocks.

As an example of the invention, Virgin gas oil of about 28 A, P. I. gravity, is subjected to conversion in a coil and drum cracking system, using a coil outlet temperature of about 900 to 920 F. and temperatures of about 870 to 900 F. and about 250 pounds pressure in the soaking drums. Heavy reflux condensate is recycled, maintaining a ratio of recycle stock to fresh feed of about 1:1. A crack per pass of about 20 to 25% may be obtained. The tar drawn from the soaking drums is flashed in a tar stripper under a pressure of atmospheric to 15 pounds. The bulk of the reflux condensate from the fractionator of the cracking unit is withdrawn to the fractionating section of the tar stripper, Gas oil obtained from the tar stripper is used as an absorption medium in an absorber in which the residual gases from the cracking system were scrubbed. The enriched refractory gas oil is charged to an independently controlled cracking unit operating on a recycle basis, using a coil and drum. A temperature of about 900 F. and about 200 pounds are maintained in the soaking drums, and a crack per pass of about 12% is used. Unstable gasolines are obtained from both units and charged to a stabilizer. 'Ihe residual gases from the accumulator drums of the units are charged to the aforementioned absorber. 'Ihe stabilizer reflux is charged to the unit operating on the refractory recycle stocks in such an amount that the charge to the furnace contained about 8 to 10% of total added normally gaseous hydrocarbons, A stable gasoline is obtained of 400 end point and about '70 to 72 octane number C. F. R. M. The yield of gasoline is about 68% when operating to about 8 A. P. I, gravity fuel oil. An increased yield of gasoline of about 10% and an increased capacity of the unit of 20% are obtained over a normal cracking operation in which there is no segregation of the refractory recycle stocks nor gas reversion used.

Obviously many modifications and variations may be made in the invention as herein set forth without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim;

1. A process for the conversion of hydrocarbon oils, which comprises passing a virgin charging stock through a primary conversion zone wherein the oil is cracked under the influence of temperature and pressure and the cracked products are separated into vapors and residuurn, passing the vapors to a pirmary fractionating zone wherein hydrocarbons of higher boiling range than the desired distillate are condensed to form a clean recycle stock, cooling the uncondensed vapors to form a cracked naphtha distillate and normally gaseous hydrocarbons, flash distilling said residuum in a tar stripper to form a cycle gas oil distillate, combining said clean recycle stock and said cycle gas oil distillate, passing at least a portion of the resulting mixture to an absorber, introducing into said absorber said normally gaseous hydrocarbons whereby the heavier constituents thereof are absorbed in the oil, subjecting the enriched oil to cracking conditions of temperature and pressure in a secondary conversion zone, separating the cracked products into vapors and residuum, passing the residuum to said tar stripper, fraotionating the vapors in a second fractionator to form a recycle stock, a cracked distillate and normally gaseous hydrocarbons, re'

turning the recycle stock to said secondary cracking Zone and introducing the last mentioned normally gaseous hydrocarbons into said absorber.

2. A process according to claim l in which an unstable cracked distillate is recovered from the system, said unstable distillate is stabilized, and a stabilizer distillate, predominating in normally gaseous hydrocarbons containing between 2 and 5 carbon atoms, is charged to the secondary conversion zone.

RICHARD F. TROW. 

